The invention relates to backflow preventer that, in an insertable housing thereof, includes a valve member located in a housing interior. The valve member sealingly rests against a valve seat in the closed position thereof while being movable from the closed position thereof into the open position thereof counter to a restoring force. The interior of the housing is provided with an interior section which has an interior cross section that is larger than the outer circumference of the valve member in the movement zone of the valve member.
From DE 37 22 665 C2, a backflow preventer is already known, which can be inserted in gas or water lines and thus in sanitation flow lines. The known backflow preventer has a valve member arranged in an outer housing. This valve member can be shifted by the restoring force of a restoring spring acting on the member counter the flow direction against the valve seat. Here, the valve member is guided in a separate guide cage located in the outer housing. This cage has guide ridges, which extend in the direction of the shifting path of the valve member, which project radially inwards, and which are connected to each other by a common base and are held on both sides in the outer housing.
The supply-side end of these guide ridges is arranged with spacing underneath the valve seat. Between the valve seat forming a seal with the valve member in the closed position on one side and the supply-side end of the guide ridges on the other side, an interior section is provided, which has an open cross section expanded relative to the outer periphery of the valve body. However, the problem arises, especially for low flow rates, which lift the valve member only slightly from the valve seat, that the valve member starts to vibrate due to the flowing fluid in the course of its shifting movement in the expanded interior section. These vibrations can strike the valve member like a bell on the outer housing, making it noticeable as an unpleasant rattling noise. This rattling noise can be heard, possibly throughout the entire building, through the sanitation-system supply line.
From GB 661 479 A, a hydraulic shock absorber is already known, which has a two-port valve in the interior of its shock-absorber housing. The two-port valve of the known shock absorber has a valve housing with an inner ring flange, which acts as a valve seat for a closing body. The closing body has, on its die, a flow-through channel, in which is provided a non-return valve active in the opposite flow-through direction. When the shock absorber moves, in the interior of the shock-absorber housing a low pressure is generated, which lifts the closing body from its valve seat until its lifting movement is limited by spring-elastic, finger-like stops projecting inwards and arranged in a radiating pattern relative to each other.
However, in the applications of a hydraulic shock absorber, those noises, which could be generated in the interior of the shock absorber just by the flowing hydraulic fluid are of no importance whatsoever. A play-free lifting movement in the radial direction is therefore not a goal—instead in the shock absorber known from GB 661 479 A, the finger-like stops should limit the lifting movement of the closing body in the axial direction caused by the low pressure.